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Versions: (draft-sarikaya-nvo3-vmm-dmm-pmip) 00 01 02 03 04 05 06 07 08 09

Network Working Group                                      L. Dunbar
Internet Draft                                             Futurewei
Intended status: Informational                           B. Sarikaya
Expires: September 26, 2020                      Denpel Informatique
                                                       B.Khasnabish
                                                        Independent
                                                          T. Herbert
                                                               Intel
                                                          S. Dikshit
                                                           Aruba-HPE
                                                      March 26, 2020



     Virtual Machine Mobility Solutions for L2 and L3 Overlay Networks
                          draft-ietf-nvo3-vmm-09

Abstract

   This document describes virtual machine mobility solutions commonly
   used in data centers built with overlay-based network. This document
   is intended for describing the solutions and the impact of moving
   VMs (or applications) from one Rack to another connected by the
   Overlay networks.

   For layer 2, it is based on using an NVA (Network Virtualization
   Authority) - NVE (Network Virtualization Edge) protocol to update
   ARP (Address Resolution Protocol) table or neighbor cache entries
   after a VM (virtual machine) moves from an Old NVE to a New NVE.
   For Layer 3, it is based on address and connection migration after
   the move.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79. This document may not be modified,
   and derivative works of it may not be created, except to publish it
   as an RFC and to translate it into languages other than English.






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   Internet-Drafts are working documents of the Internet Engineering
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   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents


   1. Introduction...................................................3
   2. Conventions used in this document..............................4
   3. Requirements...................................................5
   4. Overview of the VM Mobility Solutions..........................6
      4.1. Inter-VNs communication...................................6



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      4.2. VM Migration in Layer 2 Network...........................6
      4.3. VM Migration in Layer-3 Network...........................8
      4.4. Address and Connection Management in VM Migration.........9
   5. Handling Packets in Flight....................................10
   6. Moving Local State of VM......................................11
   7. Handling of Hot, Warm and Cold VM Mobility....................11
   8. Other Options.................................................12
   9. VM Lifecycle Management.......................................12
   10. Security Considerations......................................12
   11. IANA Considerations..........................................13
   12. Acknowledgments..............................................13
   13. Change Log...................................................13
   14. References...................................................13
      14.1. Normative References....................................14
      14.2. Informative References..................................15

1. Introduction
     This document describes the overlay-based data center networks
     solutions in supporting multitenancy and VM (Virtual Machine)
     mobility. This document is strictly within the DCVPN, as defined
     by the NVO3 Framework [RFC 7365]. The intent is to describe Layer
     2 and Layer 3 Network behavior when VMs are moved from one NVE to
     another. This document assumes that the VMs move is initiated by
     VM management system, i.e. planed move. How and when to move VM
     are out of the scope of this document. RFC7666 already has the
     description of the MIB for VMs controlled by Hypervisor. The
     impact of VM mobility on higher layer protocols and applications
     is outside its scope.
     Many large DCs (Data Centers), especially Cloud DCs, host tasks
     (or workloads) for multiple tenants. A tenant can be a department
     of one organization or an organization. There are communications
     among tasks belonging to one tenant and communications among tasks
     belonging to different tenants or with external entities.
     Server Virtualization, which is being used in almost all of
     today's data centers, enables many VMs to run on a single physical
     computer or server sharing the processor/memory/storage.  Network
     connectivity among VMs is provided by the network virtualization
     edge (NVE) [RFC8014].  It is highly desirable [RFC7364] to allow
     VMs to be moved dynamically (live, hot, or cold move) from one
     server to another for dynamic load balancing or optimized work
     distribution.
     There are many challenges and requirements related to VM mobility
     in large data centers, including dynamic attaching/detaching VMs
     to/from Virtual Network Edges (VNEs).  In addition, retaining IP


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     addresses after a move is a key requirement [RFC7364].  Such a
     requirement is needed in order to maintain existing transport
     connections.
     In traditional Layer-3 based networks, retaining IP addresses
     after a move is generally not recommended because the frequent
     move will cause fragmented IP addresses, which introduces
     complexity in IP address management.
     In view of many VM mobility schemes that exist today, there is a
     desire to document comprehensive VM mobility solutions that cover
     both IPv4 and IPv6. The large Data Center networks can be
     organized as one large Layer-2 network geographically distributed
     in several buildings/cities or Layer-3 networks with large number
     of host routes that cannot be aggregated as the result of frequent
     moves from one location to another without changing their IP
     addresses.  The connectivity between Layer 2 boundaries can be
     achieved by the network virtualization edge (NVE) functioning as
     Layer 3 gateway routing across bridging domain such as in
     Warehouse Scale Computers (WSC).


2. Conventions used in this document


      This document uses the terminology defined in [RFC7364].  In
      addition, we make the following definitions:

      VM:    Virtual Machine

      Tasks:  Task is a program instantiated or running on a virtual
               machine or container.  Tasks in virtual machines or
               containers can be migrated from one server to another.
               We use task, workload and virtual machine
               interchangeably in this document.

      Hot VM Mobility: A given VM could be moved from one server to
               another in running state.

     Warm VM Mobility:  In case of warm VM mobility, the VM states are
               mirrored to the secondary server (or domain) at a
               predefined (configurable) regular intervals.  This
               reduces the overheads and complexity, but this may also


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               lead to a situation when both servers may not contain
               the exact same data (state information)

      Cold VM Mobility:  A given VM could be moved from one server to
               another in stopped or suspended state.

      Old NVE:  refers to the old NVE where packets were forwarded to
               before migration.

      New NVE: refers to the new NVE after migration.

      Packets in flight: refers to the packets received by the Old NVE
               sent by the correspondents that have old ARP or neighbor
               cache entry before VM or task migration.

      Users of VMs in diskless systems or systems not using
               configuration files are called end user clients.

      Cloud DC:  Third party data centers that host applications,
               tasks or workloads owned by different organizations or
               tenants.


3. Requirements

   This section states requirements on data center network virtual
   machine mobility.

   Data center network should support both IPv4 and IPv6 VM mobility.

   Virtual machine (VM) mobility should not require changing VMs' IP
   addresses after the move.

   There is "Hot Migration" with transport service continuing, and
   "Cold Migration" with transport service restarted, i.e. the task
   running is stopped on the Old NVE, moved to the New NVE and the task
   is restarted. Not all DCs support "Hot Migration. DCs that only
   support Cold Migration should make their customers aware of the
   potential service interruption during the Cold Migration.

   VM mobility solutions/procedures should minimize triangular routing
   except for handling packets in flight.



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   VM mobility solutions/procedures should not need to use tunneling
   except for handling packets in flight.


4. Overview of the VM Mobility Solutions

     Layer 2 and Layer 3 mobility solutions are described respectively
     in the following sections.

4.1. Inter-VNs communication

     Inter VNs (Virtual Networks) communication refers to communication
     among tenants (or hosts) belonging to different VNs. Those tenants
     can be attached to the NVEs co-located in the same Data Center or
     in different Data centers. This document assumes that the inter-
     VNs communication is via the NVO3 Gateway as described in RFC8014
     (NVO3 Architecture). RFC 8014 (Section 5.3) describes the NVO3
     Gateway function which is to relay traffic onto and off of a
     virtual network, i.e. among different VNs.

     After a VM is moved to a new NVE, the VM's corresponding Gateway
     may need to change as well. If such a change is not possible, then
     the path to the external entity need to be hair-pinned to the NVO3
     Gateway used prior to the VM move.



4.2. VM Migration in Layer 2 Network

     Being able to move VMs dynamically, from one server to another,
     makes it possible for dynamic load balancing or work distribution.
     Therefore, dynamic VM Mobility is highly desirable for large scale
     multi-tenant DCs.

     In a Layer-2 based approach, VM moving to another NVE does not
     change its IP address. But this VM is now under a new NVE,
     previously communicating NVEs will continue sending their packets
     to the Old NVE.  Therefore, Address Resolution Protocol (ARP)
     cache in IPv4 [RFC0826] or neighbor cache in IPv6 [RFC4861] in the
     NVEs need to be updated promptly, especially for the NVEs that
     have attached VMs communicating with the VM being moved. If the VM
     being moved has communication with external entities, the NVO3
     gateway needs to be notified of the new NVE where the VM is moved
     to.





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     Such a change enables those NVEs to encapsulate the outgoing MAC
     frames with the current target NVE IP address.

     In IPv4, the VM immediately after the move should send a
     gratuitous ARP request message containing its IPv4 and Layer 2 MAC
     address in its new NVE.  This message's destination address is the
     broadcast address.  Upon receiving this message, the New NVE can
     update its cache of mapping MAC with IP. The New NVE should send a
     notification of the newly attached VM to the central directory
     [RFC7067] embedded in the NVA to update the mapping of the IPv4
     address & MAC address of the moving VM along with the new NVE
     address.  An NVE-to-NVA protocol is used for this purpose
     [RFC8014]. If an NVE has a VM being moved away or detached, the
     NVE should send an ARP scan to all its attached VMs to refresh its
     ARP Cache.

     Reverse ARP (RARP) which enables the host to discover its IPv4
     address when it boots from a local server [RFC0903], is not used
     by VMs if the VM already knows its IPv4 address (most common
     scenario). Next, we describe a case where RARP is used.

     There are some vendor deployments (diskless systems or systems
     without configuration files) wherein the VM's user, i.e. end-user
     client askes for the same MAC address upon migration.  This can be
     achieved by the clients sending RARP request message which carries
     the MAC address looking for an IP address allocation.  The server,
     in this case the new NVE needs to communicate with NVA, just like
     in the gratuitous ARP case to ensure that the same IPv4 address is
     assigned to the VM.  NVA uses the MAC address as the key in the
     search of ARP cache to find the IP address and informs this to the
     new NVE which in turn sends RARP reply message.  This completes IP
     address assignment to the migrating VM.

     Other NVEs communicating with this VM could have the old ARP
     entry. To avoid old ARP entries being used by other NVEs, the old
     NVE upon discovering a VM is detached should send a notification
     to all other NVEs and its NVO3 Gateway to time out the ARP cache
     for the VM [RFC8171]. When an NVE (including the old NVE) receives
     packet or ARP request destined towards a VM (its MAC or IP
     address) that is not in the NVE's ARP cache, the NVE should send
     query to NVA's Directory Service to get the associated NVE address
     for the VM. This is how the Old NVE tunneling these in-flight
     packets to the New NVE to avoid packets loss.

     IPv6 operation is slightly different:




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     In IPv6, after the move, the VM immediately sends an unsolicited
     neighbor advertisement message containing its IPv6 address and
     Layer-2 MAC address to its new NVE. This message is sent to the
     IPv6 Solicited Node Multicast Address corresponding to the target
     address which is the VM's IPv6 address. The NVE receiving this
     message should send request to update VM's neighbor cache entry in
     the central directory of the NVA.  The NVA's neighbor cache entry
     should include IPv6 address of the VM, MAC address of the VM and
     the NVE IPv6 address.  An NVE-to-NVA protocol is used for this
     purpose [RFC8014].

     To avoid other NVEs communicating with this VM using the old
     neighbor cache entry, the old NVE upon discovering a VM being
     moved or VM management system which initiates the VM move should
     send a notification to all NVEs to timeout the ND cache for the VM
     being moved.  When a ND cache entry for those VMs times out, their
     corresponding NVEs should send query to the NVA for an update.



4.3. VM Migration in Layer-3 Network

     Traditional Layer-3 based data center networks usually have all
     hosts (tasks) within one subnet attached to one NVE. By this
     design, the NVE becomes the default route for all hosts (tasks)
     within the subnet. But this design requires IP address of a host
     (task) to change after the move to comply with the prefixes of the
     IP address under the new NVE.

     A VM migration in Layer 3 Network solution is to allow IP
     addresses staying the same after moving to different locations.
     The Identifier Locator Addressing or ILA [I-D.herbert-nvo3-ila] is
     one of such solutions.

     Because broadcasting is not available in Layer-3 based networks,
     multicast of neighbor solicitations in IPv6 and ARP for IPv4 would
     need to be emulated. Scalability of the multicast (such as IPv6 ND
     and IPv4 ARP) can become problematic because the hosts belonging
     to one subnet (or one VLAN) can span across many NVEs. Sending
     broadcast traffic to all NVEs can cause unnecessary traffic in the
     DCN if the hosts belonging to one subnet are only attached to a
     very small number of NVEs. It is preferable to have a directory
     [RFC7067] or NVA to manage the updates to an NVE of the potential
     other NVEs a specific subnet may be attached and get periodic
     reports from an NVE of all the subnets being attached/detached, as
     described by RFC8171.



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     Hot VM Migration in Layer 3 involves coordination among many
     entities, such as VM management system and NVA. Cold task
     migration, which is a common practice in many data centers,
     involves the following steps:

     - Stop running the task.
     - Package the runtime state of the job.
     - Send the runtime state of the task to the New NVE where the
        task is to run.
     - Instantiate the task's state on the new machine.
     - Start the tasks for the task continuing from the point at which
        it was stopped.


     RFC7666 has the more detailed description of the State Machine of
     VMs controlled by Hypervisor

4.4. Address and Connection Management in VM Migration

     Since the VM attached to the New NVE needs to be assigned with the
     same address as VM attached to the Old NVE, extra processing or
     configuration is needed, such as:

     - Configure IPv4/v6 address on the target VM/NVE.
     - Suspend use of the address on the old NVE.  This includes the
        old NVE sending query to NVA upon receiving packets destined
        towards the VM being moved away. If there is no response from
        NVA for the new NVE for the VM, the old NVE can only drop the
        packets. Referring to the VM State Machine described in
        RFC7666.
     - Trigger NVA to push the new NVE-VM mapping to other NVEs which
        have the attached VMs communicating with the VM being moved.

     Connection management for the VM being moved involves
     reestablishing existing TCP connections in the new place.

     The simplest course of action is to drop all TCP connections to
     the VM across a migration.  If the migrations are relatively rare
     events in a data center, impact is relatively small when TCP
     connections are automatically closed in the network stack during a
     migration event.  If the applications running are known to handle
     this gracefully (i.e. reopen dropped connections) then this
     approach may be viable.



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     More involved approach to connection migration entails pausing the
     connection, packaging connection state and sending to target,
     instantiating connection state in the peer stack, and restarting
     the connection.  From the time the connection is paused to the
     time it is running again in the new stack, packets received for
     the connection could be silently dropped.  For some period of
     time, the old stack will need to keep a record of the migrated
     connection.  If it receives a packet, it can either silently drop
     the packet or forward it to the new location, as described in
     Section 5.

5. Handling Packets in Flight

     The Old NVE may receive packets from the VM's ongoing
     communications. These packets should not be lost; they should be
     sent to the New NVE to be delivered to the VM.  The steps involved
     in handling packets in flight are as follows:

     Preparation Step:  It takes some time, possibly a few seconds for
     a VM to move from its Old NVE to a New NVE. During this period, a
     tunnel needs to be established so that the Old NVE can forward
     packets to the New NVE. Old NVE gets New NVE address from its NVA
     assuming that the NVA gets the notification when a VM is moved
     from one NVE to another. It is out of the scope of this document
     on which entity manages the VM move and how NVA gets notified of
     the move. The Old NVE can store the New NVE address for the VM
     with a timer. When the timer expired, the entry for the New NVE
     for the VM can be deleted.

     Tunnel Establishment - IPv6:  Inflight packets are tunneled to the
     New NVE using the encapsulation protocol such as VXLAN in IPv6.

     Tunnel Establishment - IPv4:  Inflight packets are tunneled to the
     New NVE using the encapsulation protocol such as VXLAN in IPv4.

     Tunneling Packets - IPv6:  IPv6 packets received for the migrating
     VM are encapsulated in an IPv6 header at the Old NVE.  New NVE
     decapsulates the packet and sends IPv6 packet to the migrating VM.

     Tunneling Packets - IPv4:  IPv4 packets received for the migrating
     VM are encapsulated in an IPv4 header at the Old NVE. New NVE
     decapsulates the packet and sends IPv4 packet to the migrating VM.

     Stop Tunneling Packets:  When the Timer for storing the New NVE
     address for the VM expires. The Timer should be long enough for
     all other NVEs that need to communicate with the VM to get their
     NVE-VM cache entries updated.


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6. Moving Local State of VM
     In addition to the VM mobility related signaling (VM Mobility
     Registration Request/Reply), the VM state needs to be transferred
     to the New NVE.  The state includes its memory and file system if
     the VM cannot access the memory and the file system after moving
     to the New NVE.

     The mechanism of transferring VM States and file system is out of
     the scope of this document. Referring to RFC7666 for detailed
     information.

7. Handling of Hot, Warm and Cold VM Mobility
     Both Cold and Warm VM mobility (or migration) refers to the VM
     being completely shut down at the Old NVE before restarted at the
     New NVE. Therefore, all transport services to the VM are
     restarted.

     Upon starting at the New NVE, the VM should send an ARP or
     Neighbor Discovery message. Cold VM mobility also allows the Old
     NVE and all communicating NVEs to time out ARP/neighbor cache
     entries of the VM.  It is necessary for the NVA to push the
     updated ARP/neighbor cache entry to NVEs or for NVEs to pull the
     updated ARP/neighbor cache entry from NVA.

     The Cold VM mobility can be facilitated by VM management system to
     exchange the needed states between the Old NVE and the New NVE.
     The cold mobility option can be used for non-critical applications
     and services that can tolerate interrupted TCP connections.

     The Warm VM mobility refers to having the backup entities receive
     backup information at more frequent intervals, so that it can take
     less time to launch the VM under the new NVE.  The duration of the
     interval determines the effectiveness (or benefit) of Warm VM
     mobility.  The larger the duration, the less effective the Warm VM
     mobility option becomes.

     For Hot VM Mobility, once a VM moves to a New NVE, the VM IP
     address does not change and the VM should be able to continue to
     receive packets to its address(es). The VM needs to send a
     gratuitous Address Resolution message or unsolicited Neighbor
     Advertisement message upstream after each move.






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8. Other Options
     There is also a Hot Standby option in addition to the Hot
     Mobility, where there are VMs in both primary and secondary NVEs.
     They have identical information and can provide services
     simultaneously as in load-share mode of operation.  If the VM in
     the primary NVE fails, there is no need to actively move the VM to
     the secondary NVE because the VM in the secondary NVE already
     contain identical information.  The Hot Standby option is the
     costliest mechanism, and hence this option is utilized only for
     mission-critical applications and services.  In Hot Standby
     option, regarding TCP connections, one option is to start with and
     maintain TCP connections to two different VMs at the same time.
     The least loaded VM responds first and pickup providing service
     while the sender (origin) still continues to receive Ack from the
     heavily loaded (secondary) VM and chooses not to use the service
     of the secondary responding VM.  If the situation (loading
     condition of the primary responding VM) changes the secondary
     responding VM may start providing service to the sender (origin).

9. VM Lifecycle Management
     The VM lifecycle management is a complicated task, which is beyond
     the scope of this document. Not only it involves monitoring server
     utilization, balanced distribution of workload, etc., but also
     needs to manage seamlessly VM migration from one server to
     another.

10. Security Considerations
     Security threats for the data and control plane for overlay
     networks are discussed in [RFC8014].  ARP (IPv40 and ND (IPv6) are
     not secure, especially if we accept gratuitous versions in multi-
     tenant environment.

     In Layer-3 based overlay data center networks, the problem of
     address spoofing may arise.  An NVE may have untrusted VMs
     attached. This usually happens in cases like the VMs running third
     party applications.  Those untrusted VMs can send falsified ARP
     (IPv4) and ND (IPv6) messages, causing NVE, NVO3 Gateway, and NVA
     to be overwhelmed and not able to perform legitimate functions.
     The attacker can intercept, modify, or even stop data in-transit
     ARP/ND messages intended for other VNs and initiate DDOS attacks
     to other VMs attached to the same NVE.





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     This requires VM management system to apply stronger security
     mechanisms when add a VM to an NVE. VM Management system is out of
     scope of this document.

11. IANA Considerations

       This document makes no request to IANA.

12. Acknowledgments

   The authors are grateful to Bob Briscoe, David Black, Dave R.
   Worley, Qiang Zu, Andrew Malis for helpful comments.


13. Change Log


  . submitted version -00 as a working group draft after adoption

  . submitted version -01 with these changes: references are updated,
       o added packets in flight definition to Section 2

  . submitted version -02 with updated address.

  . submitted version -03 to fix the nits.

  . submitted version -04 in reference to the WG Last call comments.

  . Submitted version - 05, 06, 07, and 08 to address IETF LC comments
     from TSV area.




14. References









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14.1. Normative References

   [RFC0826]  Plummer, D., "An Ethernet Address Resolution Protocol: Or
             Converting Network Protocol Addresses to 48.bit Ethernet
             Address for Transmission on Ethernet Hardware", STD 37,
             RFC 826, DOI 10.17487/RFC0826, November 1982,
             <https://www.rfc-editor.org/info/rfc826>.

    [RFC0903]  Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A
             Reverse Address Resolution Protocol", STD 38, RFC 903,
             DOI 10.17487/RFC0903, June 1984, <https://www.rfc-
             editor.org/info/rfc903>.

    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

    [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
             DOI 10.17487/RFC2629, June 1999,  <https://www.rfc-
             editor.org/info/rfc2629>.



    [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
             "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
             DOI 10.17487/RFC4861, September 2007,  <https://www.rfc-
             editor.org/info/rfc4861>.

    [RFC7067] L. Dunbar, D. Eastlake, R. Perlman, I. Gashinsky,
             "directory Assistance Problem and High Level Design
             Proposal", RFC7067, Nov. 2013

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
             L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
             eXtensible Local Area Network (VXLAN): A Framework for
             Overlaying Virtualized Layer 2 Networks over Layer 3
             Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
             <https://www.rfc-editor.org/info/rfc7348>.







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    [RFC7364]  Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L.,
             Kreeger, L., and M. Napierala, "Problem Statement:
             Overlays for Network Virtualization", RFC 7364,  DOI
             10.17487/RFC7364, October 2014,  <https://www.rfc-
             editor.org/info/rfc7364>.

    [RFC7666] H. Asai, et al, "Management Information Base for Virtual
             Machines Controlled by a Hypervisor", RFC7666, Oct 2015.

   [RFC8014]  Black, D., Hudson, J., Kreeger, L., Lasserre, M., and T.
             Narten, "An Architecture for Data-Center Network
             Virtualization over Layer 3 (NVO3)", RFC 8014,  DOI
             10.17487/RFC8014, December 2016, <https://www.rfc-
             editor.org/info/rfc8014>.

   [RFC8171] D. Eastlake, L. Dunbar, R. Perlman, Y. Li, "Edge Directory
             Assistance Mechanisms", RFC 8171, June 2017
14.2. Informative References

    [I-D.herbert-nvo3-ila] Herbert, T. and P. Lapukhov, "Identifier-
             locator addressing for IPv6", draft-herbert-nvo3-ila-04
             (work in progress), March 2017.
























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Authors' Addresses


   Linda Dunbar
   Futurewei
   Email: ldunbar@futurewei.com

   Behcet Sarikaya
   Denpel Informatique
   Email: sarikaya@ieee.org

   Bhumip Khasnabish
   Independent
   Email: vumip1@gmail.com


   Tom Herbert
   Intel
   Email: tom@herbertland.com


   Saumya Dikshit
   Aruba-HPE
   Bangalore, India
   Email: saumya.dikshit@hpe.com





















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